【Daily Question: Pump Equipment】Weekly Summary 2018.12.9

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The last edit to this post was made by 3983596_FPPZ on 2019-1-19 at 09:45. Monday (2018.12.3): https://bbs.hcbbs.com/thread-2177819-1-1.html. The relationship between various performance parameters of a pump exists under certain conditions; other parameters change as the flow rate changes. Pump manufacturers usually represent these relationships using characteristic curves (performance curves). (D) A. Shaft power B. Head C. Flow rate D. Rotational speed. Tuesday (2018.12.4): https://bbs.hcbbs.com/thread-2179645-1-1.html. The correct statement regarding pumping devices is (C): A. The inlet pipe is generally under positive pressure, while the outlet pipe is under negative pressure. B. Centrifugal pumps installed above the water surface of the inlet tank can be started directly without the need for priming. C. Centrifugal pump systems installed above the water surface of the inlet tank must be primed before starting. D. Centrifugal pumps must be installed below the water surface of the inlet tank. Wednesday (2018.12.5): https://bbs.hcbbs.com/thread-2180752-1-1.html. A centrifugal pump is used to transport clean water at room temperature. Given that the flow rate is 50 m³/h, the head is 32 m, the shaft power is 7.9 KW, the motor power is 11 KW, and the rotational speed is 2950 RPM, then the pump’s efficiency is closest to which of the following values? (B) A. 72% B. 55% C. 52% D. 40%. Thursday (2018.12.6): https://bbs.hcbbs.com/thread-2182538-1-1.html. The performance parameter values listed on a pump’s nameplate at its designed rotational speed are generally those obtained under ( ) conditions. (F) A. When the rotational speed is at its highest B. When the flow rate is at its maximum and the head is at its highest D. When the net positive suction head is at its minimum E. When the shaft power is at its lowest F. When the pump efficiency is at its highest. Friday (2018.12.7): https://bbs.hcbbs.com/thread-2184387-1-1.html. With all other conditions remaining unchanged, when the density of the medium pumped by the pump decreases, which of the following statements is correct? (A B C I J) A. The flow rate remains unchanged. B. The head remains unchanged. C. The shaft power decreases. D. The outlet pressure remains unchanged. E. The flow rate decreases. F. The shaft power remains unchanged. G. The pump’s net positive suction head decreases. H. The head decreases. I. The outlet pressure decreases. J. The pump’s net positive suction head remains unchanged. Saturday (2018.12.8): https://bbs.hcbbs.com/thread-2192325-1-1.html. When a centrifugal pump uses ( ), it results in a decrease in the pump’s flow rate, but an increase in the pump’s shaft power. (C) A. Variable frequency speed control B. Outlet valve control C. Return bypass control D. Adjustment of the outer diameter of the impeller